292 CIRCULATORY APPARATUS. 



thickening both of the muscular coat and the endocardium. A diastolic 

 murmur is naturally generated in the contracted auriculo-ventricular 

 orifice during the cardiac diastole ; this is best heard at the heart's apex, 

 towards which the blood-current is directed. Next comes the systole. 

 During this, a portion of the blood which has passed into the ventricle, 

 is driven back into the auricle through the incompetent valve ; hence a 

 systolic murmur replacing the first sound, so far as this is due to closure 

 of the mitral valve. In this partial regurgitation of the blood from the 

 left ventricle, we have another cause of increased blood-pressure in the 

 left auricle. So that the insufficiency and the stenosis combine to cause 

 increased tension in the left auricle, and in the whole pulmonary circu- 

 lation. All the important clinical phenomena group themselves round 

 this as a centre. The increased tension is to some extent salutary, 

 inasmuch as it assists in filling the left ventricle rapidly and completely 

 during the diastole, in spite of the contraction of the mitral orifice. It 

 compensates therefore in some degree for the valvular defect. On the 

 other hand, however, it occasions congestion of the pulmonary vessels, 

 a passive hyperemia of the lungs, which leads to "brown induration" 

 of those organs (cf. Morbid Anatomy of the Respiratory Organs). The 

 second sound of the heart, so far as it is produced by the pulmonary 

 valves, appears exaggerated, owing to the increased tension of their flaps. 

 This is most distinct to the left of the sternum, on a level with the third 

 rib, where the conus arteriosus (fig. 93, d) lies nearest to the chest-wall. 

 Again, the work of the right ventricle is increased, inasmuch as it has 

 to open the tightly-stretched valves of the pulmonary artery with each 

 systole, and to pump the blood it contains into the already over-distended 

 pulmonary system. The result of this is hypertrophy of the right 

 ventricle [see § 235). The hypertrophy is associated with dilatation. 

 The right auriculo-ventricular orifice takes part in the dilatation, and 

 ultimately gets so wide that the tricuspid valve no longer suffices to 

 close it during the systole. A relative insufficiency of this valve also is 

 thus brought about; the stasis extends to .the systemic veins, and 

 leads to morbid changes in the liver, alimentary tract, kidneys, &c., 

 which we shall have to consider when we treat of the morbid anatomy 

 of these organs. A highly characteristic symptom of this relative in- 

 suflBciency of the tricuspid valve is the so-called " venous pulse," due to 

 propagation of the systolic wave into the principal veins. Stenosis with 

 insufficiency of the pulmonary valves is nearly always congenital and 

 wiU be referred to in the third section of the present chapter. Stenosis 

 with insuflaciency of the tricuspid is exceedingly rare. The presence of 

 venous pulsation is one of the chief guides to its recognition. 



F. Fibroid Patch and partial Aneurism of the Heart, 



§ 256. Chronic endocarditis leads to very different results 

 when it invades that part of the endocardium which lines the 

 cavities of the heart. The hyperplastic thickening of the con- 



